A particle beam therapy is given for treating a diseased site as a treatment target by irradiating it with a beam of charged particles (particle beam) to thereby damage a tissue of the diseased site. At that time, in order not to cause damage to the surrounding tissue so that a sufficient dose is imparted to the tissue of the diseased site, it is required to adequately control the quantity of radiation and the region of irradiation (irradiation field). As methods of controlling the irradiation field, there are those of a conventionally-used broad-beam irradiation type in which the irradiation field is formed by beam transmission through a physical limiter, and those of a scanning irradiation type which have been recently focused on and in which the irradiation field is directly formed by scanning (referred to, for example, in Patent Documents 1 to 3). In particular, in the case of the scanning irradiation type, an in-plane dose distribution can also be controlled freely, thus making it possible to impart a dose matched to a state of the diseased site.
In any of these cases, a controller for controlling en electromagnet is likely to cause its failure, because it is being placed in an environment where many neutrons, etc., are produced in order to control a trajectory of the particle beam and the region of irradiation. Accordingly, as shown in Patent Documents 4 to 7, it is conceivable to make redundant a line of the controller to thereby detect the failure.